Dye-sensitized solar cells said to be a next-generation solar cell is a semi-permanent solar cell developed by using a dye which is a polymer material to produce and absorb electrons, and recently, they are gaining attention as a new environmental renewable energy source. Dye-sensitized solar cells use a transparent glass substrate and can freely display colors according to the type of dye and thus have an aesthetic value, and can be made in different sizes, so they are expected to be easily used over a wide range of applications, and are of high use. However, because efficiency is still low at the current level of development, they are not fully used in all possible applications, and large-area dye-sensitized solar cells are produced on a trial basis and some are being used for interior applications on windows or walls. Accordingly, the potential for development of dye-sensitized solar cells is high, and in this instance, large-area fabrication of dye-sensitized solar cells is an important factor of development.
In addition to a dye, dye-sensitized solar cells use an electrolyte as an electron transport channel, and liquid electrolytes differ in components according to the type of dye. For electrolyte impregnation, a partition wall is needed to prevent an electrolyte from leaking, and DuPont™ Surlyn film which is a polymer material was used as a conventional sealing material for a dye-sensitized solar cell. However, Surlyn film has limitations in the respect that it has low mechanical durability, is difficult to achieve precise bonding because it is of film type, and is prone to react with oxygen or water due to the properties of organics. Particularly, for large-area fabrication, precise bonding and high mechanical durability for maintaining adhesion of a large-area substrate is required, but Surlyn film is difficult to satisfy these requirements.
To solve the problem, glass is used as a sealing material to ensure the mechanical durability and allow uniform bonding by a screen printing method using a glass paste. Furthermore, formulation free of alkali and transition metal is needed to minimize reactivity of glass with an electrolyte in order to ensure the chemical durability.
On the other hand, TiO2 is used as an electron transport material of a dye-sensitized solar cell, but TiO2 changes in crystal structure depending on the phase, and in this instance, in the case of phase having the greatest electron transport ability, a phase transition occurs at 550° C., and accordingly, there is a need for glass formulation that can be used at 550° C. or less.
There are results of studies using, as a sealing material, commercial glasses conventionally used, such as boro-silicate or soda-lime, but high process temperature is required, and thus, glass production was difficult and uniform bonding was not easy. Furthermore, there were instances of using a laser to replace high process temperature, but precise laser control is difficult, so difficulty in uniform bonding still exists.
Moreover, commercial glass formulations include some alkali elements and transition metals, and this causes a problem as well.